The Emission Spectra of Pristine and Electron-Irradiated InGaN UV LEDs at Different Temperatures and Injection Currents

The electroluminescence profile of the LED based on the InxGa1−xN (x ≤ 0.1) solid solutions was studied in detail. The emission spectrum at 300 K consists of three bands: the main UV peak at 370 nm originates from the recombination transitions in quantum wells (QWs), and two other weak bands at 550 nm (yellow) and 770 nm (red) are due to structural defects. Irradiation with 2 MeV electrons causes a drop of intensity of all three bands and gives a rise to another band at 420 nm. While the latter is manifestation of the radiation defects introduced into the QWs region, the former is accompanied by a higher current due to non-radiative transitions allowed when the quasi-Fermi level shifts toward the region of higher density of the zone tails. The temperature of the p–n junction at the nominal operating current of 20 mA was evaluated to be about 525 K (252 ℃). The optical measurements of the LEDs in the 77‒300 K temperature range and for the injection currents varying from 10 µA to 20 mA allowed for studying the fine structure of all three bands at low temperatures. In particular, the observed doubling of the UV emission maximum at 77 K is ascribed to the phonon repetition of the main emission line.